This application is Part B of a proposal for a competing renewal of the Pittsburgh component of the Multicenter AIDS Cohort Study (MACS) Cooperative Agreement (1UO1-AI-35041), the companion to the Part A composite proposal that is being submitted by CAMACS. This request is for an additional five years of support for clinical follow-up and laboratory testing of the original and recently recruited cohort of MSM in the Pittsburgh MACS. The current priority of the MACS is to enhance our epidemiologic and pathogenesis information in relation to treatment intervention. We need to describe the long-term patterns of therapy use that are consequential in terms of treatment efficacy. Our specific aims emphasize cohort retention and maintenance, biological specimen procurement and central lipid/insulin/glucose testing for dyslipidemia, diabetes, lipodystrophy and cardiovascular disease for the MACS. These are: (1) To characterize the evolving natural history of treated HIV infection and identify the determinants and trends of long-term HIV-related outcomes in the era of HAART. We will determine the effect of anti-retroviral therapies on disease incidence, surrogate markers and survival expectation. This includes special emphasis on our recently expanded cohort of young, African-American MSM, who were underrepresented in the original MACS cohort, yet maintain an inordinately greater prevalence of HIV infection in the USA. (2) To maintain the longitudinally collected epidemiological data and biological specimen repository framework of the Pittsburgh MACS as a platform to facilitate natural history and pathogenesis studies. (3) To perform the required clinical and laboratory testing of HIV seropositive and seronegative MSM in the Pittsburgh MACS. (4) To perform cardiovascular testing (Electron Beam Computed Tomography [EBCT], carotid intima media thickness [IMT], and EKG testing) on a sub-sample of the MACS to address key questions related to risk of cardiovascular disease among HAART recipients. We believe that through these aims, as well as through substudies on the immunopathogenesis of HIV infection that are closely linked to the Pittsburgh MACS, we will significantly contribute to the scientific agenda and goals of the MACS.